1. Field of the Invention
The present invention relates to the preparation of crimped tow using a stuffer box in combination with a pair of crimping rollers to feed molded tow to the stuffer box and in addition to these elements, a pair of molding rollers for molding the tow before the tow enters the crimping rollers. The addition of the molding rollers not only improves the uniformity of the crimped tow, but also improves the edge quality of the tow and reduces processing runability malfunctions resulting from the sliding resistance of the crimped tow through the stuffer box. More specifically, in one embodiment, a tow of parallel filaments is molded into a rectangular cross section by a pair of parallel, rotatable molding rollers cooperating with a pair of side plates arranged to define a rectangular mold nip through which the tow is fed. In addition to molding the tow, the molding rollers pull the tow to the molding rollers and squeeze the tow to remove any residual liquid finish from the surface thereof. Subsequent to the molding rollers, the molded tow is fed through a similar rectangular nip defined by the crimping rollers. From the crimping rollers, the molded tow material is fed into a stuffer box wherein it is crimped.
2. Prior Art
In prior art apparatuses, continuous filament tow is typically pulled, dewatered, rectangularly molded and fed by a single pair of smooth, cylindrical parallel, rotatable crimping rollers in conjunction with side plates into a rectangular stuffer box, referred to in some references as a crimping chamber. The stuffer box generally forms a substantially rectangular closed pressure zone having a weighted discharge door or flapper at the exit thereof. As the tow is fed by the crimping rollers into the stuffer box, the filaments loop back and forth upon itself and against the resistance of the inner walls of the stuffer box, forming a crimped wad. This wad is compressed in its passage through the stuffer box by the friction of the side walls and the weighted discharge flapper. The action of the crimping rollers in continuously feeding tow into the chamber produces crimps in the tow which can be later effectively set by heat or fluid treatment. The crimped tow is discharged from the stuffer box at a rate proportionate to the infeed of the crimping rollers.
Each of the crimping rollers is rotatable in opposite directions and positioned along with a side plate at each end thereof to form a rectangular nip to allow the tow to be rectangularly molded between the two rollers and two side plates. By this action, the tow is pulled through the nip, and molded, conforming to the rectangular configuration of the space between the crimping rollers and side plates, as well as squeezing any hydraulic finish from the tow.
The crimping rollers are generally arranged such that one of the rollers is adjustable, for example, by a hydraulic cylinder while the other roller is fixed. For the rollers to perform all the functions of pulling, molding, dewatering and feeding the tow requires a significant force applied by the adjustable roller against the tow material. In particular, for a 250 mm tow, between 12 and 15 tons of force are applied to the adjustable roller to accomplish all the desired functions. This high force in the nip results in decreased life of the equipment parts such as the bearings and has been found to damage the tow material including damage to the filaments. One type of damage is filament distortion, for example changing the configuration of the filaments from round to oblong which is undesirable. Furthermore, it has been found that the high nip forces press the tow material against the side plates resulting in burning or fusion of the material at the side plates. This fusion results from elevated temperatures of the tow material being excessively pressured against the side plates.
Optimally crimped tow material is produced when resistance to the rectangularly molded tow by walls of the stuffer box is evenly distributed. One factor in achieving even resistance is by feeding uniformly molded tow material into the stuffer box. This requires the preceding crimping rollers to mold the tow material to have a uniform rectangular cross section. When the molded tow is nonuniform, uneven resistance occurs between the tow and the walls of the stuffer box resulting in uneven resistance to the feeding of the tow into the stuffer box. The condition induces slack in the tow entering the stuffer box further compounding the problem. Conditions resulting from the increased resistance to the incoming tow material is erratic operation of the crimping apparatus and nonuniform crimping of the tow. Hence, it is desirous for the crimping rollers to feed uniformly rectangular molded tow to the stuffer box.
In another apparatus for crimping tow, feed rollers have been installed prior to the crimping rolls for the purpose of pulling and dewatering the tow. Such feed rollers are not pressurized as the crimping rollers and provide limited molding of the tow. Although such feed rollers are known to satisfactorily perform these two functions, their use have proved unsatisfactory in improving the uniformity of the molded tow. It has been found the problem of nonuniformly molded tow is still fed from the crimping rollers to the stuffer box resulting in the resistance against such feeding as described above. Adding the additional feeding rollers has been found to result in the tow being thinned out at the lateral edges thereof which is known as doglegging. It is believed by the inventor that the thinning of the tow of the lateral edges results in loss of crimp because of the reduced contact of the lateral edges with the crimping rollers.
The following references are directed to various apparatuses used for crimping filament or fiber tow that include at least a stuffed box and crimping rollers.
U.S. Pat. No. 3,353,239 to Heijnis discloses a method and apparatus for crimping tow. Prior to entering a conventional stuffer box crimping apparatus which includes a crimping roller and stuffer box, the tow is passed through a pair of guide rollers designated 2. The improvement disclosed in this patent is with respect to the crimping rollers having ridged surfaces to better grip the tow and crimp the tow in a direction perpendicular to the crimp produced in the stuffer box. It is further disclosed that the guide rollers may also have a similar surface configuration as the crimping rollers. The use of the ridged or curved surface configuration is stated to improve the bite of the roller surfaces and favorably influence the multi-directional crimp produced in the tow. A nonuniform clearance or nip results from such surface configurations.
U.S. Pat. No. 4,004,330 to Stanley discloses a crimping apparatus for stuffer crimping a textile tow material by use of a conventional stuffer box crimper. Included in the crimper is one additional roller (17" in FIG. 7) mounted parallel and contiguous with the peripheral surface of the crimping rollers. The additional roller serves to improve the feed of the tow to the nip of the crimping rollers.
U.S. Pat. No. 4,095,318 to Abbott et al generally discloses a crimping apparatus shown in FIGS. 1 and 2 including a stuffer box, crimping rollers and feed rollers designated 16. The feed rollers and crimping rollers ar driven by the gear system 28 connected back to a motor 21.
U.S. Pat. No. 3,813,740 to Heijnis discloses a crimping apparatus for stuffer box crimping a filament or fiber tow of at least 5,000 total denier. Tow, prior to entering a conventional stuffer box crimper which includes a pair of crimping rollers and stuffer box, is passed through a series of gear wheels. These geared wheels mold the tow into a tow band having a more parallel alignment to insure uniformity and excess of crimp of the tow in a crimper housing.
European Patent Application 0 159 285 A2 to Okada discloses a crimping apparatus for stuffer box crimping a filament or fiber tow including a pair of side plates coacting with the crimping rollers to define a rectangular nip through which the tow is passed. The molded tow is then passed to an adjacent stuffer box.
Improvements disclosed in the prior art are directed to improving the feeding of the tow material to the crimping rollers, but not the rectangular molding of the tow material prior to entering the crimping rollers. These improvements are not particularly advantageous to overcome the problems of achieving uniformly crimped tow material. When additional rollers are added to pull the tow material and to dewater it, for example, improved mold uniformity of the tow material is not achieved because the crimping rollers are still totally performing the molding step. Therefore, improved feeding of the tow material to the crimper rollers does not improve the overall mold uniformity of the tow material. In fact, it has been seen that improved feeding may result in additional problems of processing the tow material.
In addition to improving the uniformity of the crimped tow material, it is desirable to improve the apparatus by reducing the applied forces to the crimper rollers. Forces of 10 to 15 tons are currently applied to crimper roller to allow the rollers to pull, dewater, mold and feed the tow. Lower forces not only reduce equipment wear, but also improves the quality of the tow material by decreasing the deformation of the filaments within the tow. Furthermore, fusion of the lateral sides of the tow is reduced.
There remains a need to develop an apparatus for stuffer box crimping which will not only improve the moldability of the tow material, but also improve the processing of the tow material, so that the overall quality of the crimped tow material is improved.
It is a further aim or aspect of the present invention to not only improve the quality of the stuffer box crimped tow material, but also produce the crimped to material being uniform nondeformed filaments by significantly reducing the forces applied to the crimper rollers.